Formation of high strength electroplated filaments

ABSTRACT

1. IN THE PROCESS FOR PRODUCING A PLATED FILAMENT WHEREIN A POLYMERIC FILAMENT, HAVING A NON-MACROPOROUS SURFACE, IS TREATED WITH AN ORGANIC SOLVENT SOLUTION OF MATERIAL SELECTED FROM ELEMENTAL WHITE PHOSPHORUS AND LOW OXIDATION STATE PHOSPHORUS COMPOUNDS, IN WHICH THE ORGANIC SOLVENT OF SAID SOLUTION IS ONE WHICH IS CAPABLE OF SWELLING THE SURFACE OF SAID FILAMENT WITHOUT DETRIMENTALLY AFFECTING IT, THE RESULTING FILAMENT IS TREATED WITH A METAL SALT OR A COMPLEX THEREOF IN WHICH THE METAL IS SELECTED FROM GROUP IB, IIB, IVB, VB, VIB, VIIB, VIII OF THE PERIODIC TABLE AND THE RESULTING TREATED FILAMENT IS THEN ELECTROPLATED, THE IMPROVEMENT WHICH COMPRISES EFFECTING THE ELECTROPLATING SO THAT THAT A PORTION OF THE FILAMENT WITHIN THE PLATING BATH IS MAINTAINED FREE OF DEFORMATION TENSIONS AND CHANGES IN DEFORMATION TENSIONS WHICH CAUSE RANDOM NUCLEATION OF THE METAL BEING ELECTROLYTICALLY DEPOSITED, WHEREBY AN ELECTROPLATED FILAMENT IS FORMED HAVING ON ITS SURFACE AN ADHERENT, ELECTROLYTICALLY DEPOSITED METAL COATING HAVING AN ORDERED NUCLEATION.

Patented (Jet. 22, 1974 3,843,493 FORMATION OF HIGH STRENGTH ELECTROPLATED FILAMENTS George T. Miller, Lewiston, N.Y., assignor to Hooker Chemical Corporation, Niagara Falls, N.Y.

No Drawing. Continuation-impart of application Ser. No. 74,515, Sept. 22, 1970, which is a continuation-in-part of application Ser. No. 860,415, Sept. 23, 1969 both now abandoned. This application Mar. 6, 1972, Ser.

Int. Cl. C23b 5/60 US. Cl. 204 7 Claims ABSTRACT OF THE DISCLOSURE This application is a continuation-in-part of copending application Ser. No. 74,515, filed Sept. 22, 1970, Which application is a continuation-in-part of Ser. No. 860,415, filed Sept. 23, 1969 and both now abandoned.

This invention relates to an improved process for the production of high strength filaments and more particularly it relates to the production of high strength filaments by the treatment of filaments formed of polymeric or other substantially non-conductive materials.

In recent years, increasingly greater use has been made of plastic or polymeric materials as substitutes for metals in various structural applications, because of the lower cost, lighter weight and the greater versatility of forming or molding of these materials. In many instances, however, it has been found to be desirable to include reinforcing the material in these plastic or polymeric structures, for added strength. Frequently, these reinforcing materials have been in the form of metallic filaments or fibers, although the cost and weight of these greatly diminish the advantages obtained in using the plastic or polymeric materials as structural elements. Attempts to utilize fibers or filaments of polymeric materials rather than metal have generally not been successful, primarily due to the appreciably lower tensile strength of the polymeric materials, as compared to metal.

Although numerous processes have recently been developed for the treatment of polymeric and similar nonconductive substrates to make them receptive to an elec troplated metallic coating, attempts to utilize these techniques on polymeric fibers or filaments, so as to increase their tensile strength, have generally not been successful. Difiiculties have been encountered not only in forming an adherent bond with the metal coating but also in the lack of sufiicient flexability in the plated article.

It is, therefore, an object of the present invention to provide an improved process for the metal coating of fibers and filaments of polymeric and other substantially non-conductive materials.

A further object of the present invention is to provide an improved process for producing high-strength fibers or filaments which have a higher ratio of tensile strength to weight than do metallic fibers or filaments.

These and other objects will become apparent to those skilled in the art from the description of the invention which follows.

Pursuant to the above objects, the present invention includes a process for the treatment of polymeric filaments which comprises treating a polymeric filament with a material selected from elemental white phosphorus and low oxidation state phosphorus compounds, treating the resulting filament with a metal salt or complex thereof and, thereafter, electroplating the resulting treated filament with a metal while maintaining the filament free of deformation tension which is sufiicient to cause random nucleation of the electrolytically deposited metal. By this method, high strength filaments or fibers are produced which have a ratio of tensile strength to Weight which is appreciably greater than that of metal fibers or filaments.

More specifically, the process of the present invention is applicable to various plastic or polymeric substrates in the form of a filament or fiber. Additionally, other substantially non-metallic or non-conducting substrates which may be formed into fibers or filaments may also be satisfactorily treated, including cellulosic and ceramic materials, such as cloth, paper, wood, cork, porcelain, leather, porous glass, asbestos and the like. Of these, the plastic or polymeric materials are preferred and particular reference will hereinafter be made thereto.

Typical plastics or polymers to which the process of this invention is applicable include the homopolymers and copolymers of ethylenically unsaturated aliphatic, alicyclic and aromatic hydrocarbons such as polyethylene, polypropylene, polybutene, ethylenepropylene copolymers; copolymers of ethylene or propylene or with other olefins, polybutadiene; polymers of butadiene, polyisoprene, both matural and synthetic, polystyrene including high impact polystyrene and polymers of pentene, hexene, heptene, octene, Z-methylpropene, 4-methyl-hexene-l, bicyclo- (2.2.l)-2-heptene, pentadiene, hexadiene, 2,3-dimethylbutadiene-1,3,4-vinylcyclohexene, cyclopentadiene, methylstyrene, and the like. Other polymers useful in the invention include polyhalogenated hydrocarbon polymers, including fiuoro polymers such as polytetrafluoroethylene; polysilicone and polyhalogenated silicones; polyindene, indenecoumarone resins; polymers or acrylate esters and polymers of methacrylate esters, acrylate and methacrylate resins such as ethyl acrylate, n-butyl methacrylate, isobutyl methacrylate, ethyl methacrylate and methyl methacrylate; alkyd resins; cellulose derivatives such as cellulose, hydroxyethyl cellulose, methyl cellulose and sodium carboxymethyl cellulose; epoxy resins; furan resins (furfuryl alcohol or furfural-ketone); hydrocarbon resins from petroleum; isobutylene resins (polyisobutylene); isocyanate resins (polyurethanes); melamine resins such as melamine-formaldehyde and melamine-ureaformaldehyde; oleo-resins; phenolic resins such as phenolformaldehyde, phenolic-elastomer, phenolic-epoxy, phenolic-polyamide, and phenolic-vinyl acetals; polyamide polymers, such as polyamides, polyamide-epoxy and particularly long chain synthetic polymeric amides containing recurring carbonamide groups as an integral part of the main polymer chain; polyacryl amides; polysulfones; polyester resins such as unsaturated polyesters of dibasic acids and dihydroxy compounds, and polyester elastomer and resorcinol resins such as resorcinol-formaldehyde, resorcinol-furfural, resorcinol-phenol-formaldehyde, resorcinol-polyamide and resorcinol-urea; rubbers such as natural rubber, synthetic polyisoprene, reclaimed rubber, chlorinated rubber, polybutadiene, cyclized rubber, butadiene-acrylonitrile rubber, butadiene-styrene rubber, and butyl rubber; neoprene rubber (polychloroprene); polysulfides (Thiokol); terpene resins; urea resins; vinyl resins such as polymers of vinyl acetal, vinyl acetate or vinyl alcohol-acetate copolymer, vinyl alcohol, vinyl chloride, vinyl butyral, vinyl chloride-acetate copolymer, vinyl pyrrolidone and vinyldene chloride copolymer, such as a copolymer of vinylidene chloride and vinyl chloride (Saran); polyformaldehyde; polyethers, such as polyphenylene oxide, polymers of diallyl phthalates and phthalates; polycarbonates of phosgene or thiophosgene and dihydroxy compounds such as bisphenols, thermo plastic polymers of bisphenols and epichlorohydrin (tradenamed Phenoxy polymers); graft copolymers and polymers of unsaturated hydrocarbons and an unsaturated monomer, such as graft copolymers or polybutadiene, styrene and acrylonitrile, commonly called ABS resins; ABS-polyvinyl chloride polymers; acrylic polyvinyl chloride polymers; and any other suitable natural and synthetic polymers.

The polymers can be used in the unfilled conditions, or with fillers such as glass fiber, glass powder, glass beads, asbestos, talc and other mineral fillers, wood flour and other vegetable fillers, carbon in its various forms, dyes, pigments, waxes and the like. In general, the only requirement is that these plastic or polymeric materials are in the form of a filament or fiber when they are treated.

As has been noted, the substrates treated by the method of the present invention are in the form of filaments, fibers, or the like. For convenience, hereinafter reference will be made to the treatment of filaments but it is to be understood that this term includes not only filaments, but also fibers, strands, and similar configurations. The filaments treated are of a substantially circular cross-section, having a substantially smooth, non-macroporous, outer surface and a diameter which is not substantially in excess of about mils. Preferably, the diameter of the filaments are from about 0.5 to 4 mils.

As has been indicated hereinabove, the outer surface of the filaments treated in accordance with the method of the present invention is non-macroporous. By this, it is meant that the surface is either substantially non-porous or is substantially free of pores which are of a size substantially in excess of about 10 microns. Thus, the outer surface of the filament is either micro-porous in nature or even substantially non-porous. In this regard, it is to be noted that unlike many of the presently available commercial processes for the treatment of polymeric surfaces, which process utilize a chemical and/ or mechanical pretreatment of the polymer surface to make it macroporous, the method of the present invention is utilized on the filament surfaces which are non-macroporous and chemical or physical etching steps or other treatments to effect keying into the polymer, are not required to obtain an adherent metallic deposit.

In carrying out the process of the present invention, the polymeric substrate, in the form of a filament, is treated with elemental white phosphorus or low oxidation state phosphorus compounds and the resulting surface is then treated with a metal salt or metal salt complex. This process is described in detail in copending applications Ser. No. 839,080, filed July 3, 1969; Ser. No. 23967 filed Mar. 30, 1970; Ser. No. 142,053 filed May 10, 1971; and US. Pats. 3,556,956 and 3,629,922, which disclosures are hereby incorporated by reference.

The treatment with elemental white phosphorus, which includes the various impure or commercial grades sometimes referred to as yellow phosphorus, can be effected when the phosphorus is in the vapor phase, is a liquid, or is dissolved in a solvent. Suitable solvents or diluents for the elemental phosphorus are solvents which dissolve elemental phosphorus and which preferably swell the surface of the polymer without detrimentally affecting the surface of the polymer. Suitable solvents which may be used are the halogenated hydrocarbons, including those which are perhalogenated, and aromatic hydrocarbon solvents. Exemplary of the halogenated hydrocarbon solvents are chloroform, methylchloroform, dichloroethylene, trichloroethylene, perchloroethylene, ethylchloroform, phenylchloroform, trichloroethane, dichloropropane, ethyldibromide, ethylchlorobromide, propylene dibromide, monochlorobenzene, monochlorotoluene, and the like. Exemplary of suitable aromatic hydrocarbons are benzene, toluene, xylene, ethylbenzene, naphthalene and the like.

The solution concentration is generally in the range from about 0.0001 weight percent of phosphorus based on the weight of the solution up to a saturated solution, and preferably from about 0.1 to about 2.5 percent. Generally the temperature is in the range of about 30 to 135 degrees centigrade, but preferably in the range of about 50 to 100 degrees centigrade. The contact time varies depending on the nature of the substrate, the solvent and temperature, but is generally in the range of about 1 second to 1 hour or more, preferably in the range of about 1 to l0 minutes.

Alternatively, the substrate can be subjected to at least one low oxidation state phosphorus compound, i.e., wherein the phosphorus has a valence of less than 5, preferably in a solvent. Suitable low oxidation state compounds are trihydroxymethyl phosphine; phosphorus sesquisulfide; P H phosphine, diphosphine, hypophosphorus acid and salts thereof of the metals of Groups I, II and III; phosphorus acid and the salts thereof of the metals of Groups I, II and III, and low oxidation state phosphorus compounds prepared by reacting elemental phosphorus with a suitable nucleophilic reagent or organo metallic compound (including Grignard reagents). Suitable nucleophilic reagents include basic compounds having an unshared pair of electrons on a carbon, oxygen, nitrogen, sulfur or phosphorus atom. The preferred nucleophilic reagents have the formula MZ wherein M is an alkali metal or alkaline earth metal and Z is hydroxide, alkoxide, amide, sulfite, thiosulfate, mercaptide, cyanate, thiocyanate, cyanide, azide, and the like.

When phosphorus sesquisulfide, which is the preferred low-oxidation state phosphorus compounds, is employed in the process it can be utilized as a vapor, or liquid or may be dissolved in a solvent. Suitable solvents or diluents for the phosphorus sesquisulfide are solvents that dissolve the phosphorus sesquisulfide and which preferably swell the surface of the substrate without detrimentally afiecting it. Suitable solvents are the halogenated hydrocarbons, including the perhalogenated hydrocarbons, and aromatic hydrocarbon solvents as have been indicated hereinabove.

When a solution of phosphorus sesquisulfide is employed in the process, the solution concentration is generally in the range from about 0.000 1 weight percent ofphosphorus sesquisulfide based on the Weight of the solution up to a saturated solution, and preferably from about 0.5 to about 2.5 percent. Prior to contacting the substrate with the phosphorus sesquisulfide, liquid or solution, the surface of the substrate should be clean. When a solution is used, the solvent generally serves to clean the surface. A solvent wash may be desirable when liquid phosphorus sesquisulfide is employed. The phosphorus sesquisulfide treatment is generally conducted at a temperature below the softening point of the substrate, and below the boiling point of the solvent, if the solvent is used. Generally, the temperature is in the range of about zero degrees to 135 degrees centigrade, but preferably in the range of about 15 to degrees centigrade. The contact time varies depending on the nature of the substrate, the solvent and temperature, but is generally in the range of about one second to one hour or more, preferably in the range of about one to twenty minutes. The foregoing conditions described with respect to phosphorus sesquisulfide, generally also apply for the other phosphonic compounds.

The substrate can, if desired, be subjected to the solvent prior to subjection to the phosphorus or low oxidation state phosphorus compound in order to improve the quality of the resulting metal coating. It has been found that subjection of the substrate to the solvents hereinbefore disclosed prior to subjection to the phosphorus or phosphorus sesquisulfide has a very marked effect on the adhesion of the final metal plated article. The temperature of the solvent is directly related to the adhesion realized. Generally, the temperature is in the range of about 30 degrees centigrade to the boiling point of the solvent, preferably about 50 to degrees and higher than the temperature of the solution of phosphorus or phosphorus compound, if a solution is used. The contact time varies depending on the nature of the substrate, solvent and temperature but preferably is about one to fifteen minutes.

As a result of treatment with phosphorus or low oxidation state phosphorus compounds, the phosphorus or low oxidation state phosphorus compounds are deposited at the surface of the substrate. By this is meant that they can be located on the surface, embedded in the surface and embedded beneath the surface of the substrate. The location of the elemental phosphorus or phosphorus compound is somewhat dependent on the action of the solvent on the surface if one is used.

Following the treatment with elemental phosphorus or low oxidation state phosphorus compound, the substrate can be rinsed with a solvent and can then be dried by merely exposing the substrate to the atmosphere or to inert atmospheres such as nitrogen, carbon dioxide, and the like, or by drying the surface with radiant heaters or in a conventional oven. Drying times can vary considerably, for example from 1 second to 30 minutes or more, preferably 5 seconds to minutes, and preferably 5 to 120 seconds. The rinsing and drying steps are optional.

The thus-treated substrate is thereafter subjected to a solution of a metal salt or a complex of a metal salt which is capable of reacting with the elemental phosphorus to form a metal phosphide, or capable of reacting with the low oxidation state phosphorus compound to form a metalphosphorus coating. The term metal phosphide, as used herein means the metal-phosphorus coating which is formed at the surface of the substrate, the term metalphosphorus coating means the coating which is formed at the surface of the substrate and the term metal-phosphorus-sulfur compound means the metal-phosphorus-sulfur coating which is found at the surface of the substrate. The metals generally employed are those of Group IB, IIB, IVB, VB, VIB, VIIB and VIII of the Periodic Table appearing on pages 6061 of Langes Handbook of Chemistry (revised 10th Ed.). The preferred metals are copper, chromium, manganese, cobalt, nickel, titanium, zirconium, vanadium, tantalum, cadmium, tungsten, molybdenum, silver, zinc and the like.

The metal salts that are used can contain a wide variety of anions. Suitable anions include the anions of mineral acids such as sulfate, chloride, nitrate, phosphate, chlorate, perchlorate, and the like. Also useful are the anions of organic acids such as formate, acetate, citrate, stearate, and the like. Generally, the anions of organic acids contain 1 to 18 carbon atoms. Some useful metal salts include copper sulfate, copper chloride, nickel sulfate, nickel chloride, and nickel cyanide.

The metal salts can be complexed with a complexing agent that produces a solution having a basic ph 7). Particularly useful are the ammoniacal complexes of the metal salts in which 1 to 6 ammonia molecules are complexed with the foregoing metal salts. Typical examples include NiSO .6NH NiCl .6NH Ni(C H OH) .6N',I-I CuSO .6NH CuCl .6NH NiSO .3NH CuSO .4NH and the like. Other useful complexing agents include quinolines, amines and pyridine.

The foregoing metal salts and their complexes are used in ionic media, preferably in aqueous solutions. However, non-aqueous media can be employed such as alcohols, for example methanol, ethanol, butanol, and the like. Mixtures of alcohol and water can be used and ionic mixtures of alcohol with other miscible solvents of the types disclosed hereinbfeore are also useful. The solution concentration is generally in the range from about 0.1 weight percent metal salt or complex based on the total weight of the solution up to a saturated solution, preferably from about 1 to about 10 weight percent metal salt or complex. The pH of the metal salt or complex solution can range from about 4 to 14, but is generally maintained in the basic range, i.e., greater than 7, and preferably from about 10 to about 13. Generally, the contact temperature is in the range of about 0 to 110 degrees cetigrade, preferably from about 20 to degrees centigrade. The time of contact can vary considerably depending on the nature of the substrate, the characteristics of the metal salts employed and the contact temperature. However, the time of contact is generally in the range of about 0.1 to 30 minutes, preferably from about 5 to 10 minutes.

It has further been found that where the filament is treated with elemental phosphorus, rather than a low oxidation state phosphorus compound, the quality of the resulting metallic phosphide can be improved by subjecting the substrate first to a solution of elemental while phosphorus as hereinbefore described and thereafter to molten elemental while phosphorus. Generally, the substrate is subjected to the solution of elemental phosphorus for from about 1 second to about 1 hour, preferably 1 to about 10 minutes, and is thereafter subjected to the molten phosphorus for from about 1 second to about 1 hour, preferably 0.5 to about 10 minutes. The resulting substrate is thereafter subjected to a metal salt or complex thereof as described hereinbefore.

It has also been found that when a filament treated with phosphorus or low oxidation state phosphorus compounds and then a metal salt or complex, as described hereinbefore, is thereafter subjected to a second solution of a metal salt or complex thereof wherein the metal lies between silver and platinum inclusive in the electromotive series, the treated substrates can be stretched or flexed Without losing their conductivity. The metals of the second solution are silver, gold, palladium and platinum. The second metal salt bath can contain the metals as salts of the anions disclosed hereinbefore and can be complexed by the complexing agents described hereinbefore. Typical metal salts or complexes thereof employed in the second metal salt bath include silver nitrate, silver acetate, silver salicylate, silver perchlorate, Au O Au(CN) .3H O, PtCl PtBr platinum sulfate, chloroplatinic acid, and the like. The solution concentrations, subjection temperatures and contact times are as described hereinbefore with respect to the first metal salt bath. The metal of the second metal salt or complex thereof is different from the metal of the first metal salt or complex thereof.

Filaments which have been treated by the processes hereinbefore described can be employed as high strength filaments after being electroplated by a modification of the processes known in the art. The article is generally employed as the cathode and the metal desired to be plated is generally dissolved in an aqueous plating bath although other media can be employed. Generally, a soluble metal anode of the metal to be plated can be employed. In some instances, however, a carbon anode or other inert anode can be used. Suitable metals, solutions and conditions for electroplating are described in Metal Finishing Guidebook Directory for 1967, published by Metals and Plastics Publications, inc., Westwood, NJ. It is well known in these plating processes, that the electroplatc metal is nucleated on the substrate in a random order. It has now been found, however, that in the present process, an ordered nucleation can be effected if the treated filament is not subjected to deformation tension in the area of deposition during the electroplating process. This means that the treated filament cannot be touched, stretched or flexed during the electroplating process. Any deformation tension, even momentary tension such as touching the sides of the electroplating vessel, will initiate random nucleation and prevent the production of high strength filaments. The filament being plated can be supported outside of the area of the deposition and can be electroplated batchwise or continuously. If the filament is to be continuously plated, care must be taken not to introduce deformation tension in the area of deposition. It is preferred to use purified solutions and not to employ agitation therein. However, agitation can be tolerated so long as it does not cause random nucleation. It is also preferred to use direct current or pulsating direct current or alternating current superimposed on direct current. Because the nucleation on the filament grows orderly from the preceding point of deposition rather than indiscriminately from numerous points of nucleation, a greater potential than normally used for electroplating is employed. Typically, the potential employed will be from about 3 to about volts.

It is to be understood, with regard to carrying out the electroplating of the treated filament so that it is not subjected to deformation tension during the electroplating, that this means that no changes in the deformation tension of the filament are effected during the electroplating. Thus, in a continuous plating operation, the filament may be subported externally ofthe plating bath and placed under sufficient tension to pass it through the bath at whatever speed is desired. In so doing, however, the tension imparted to thefilament should not be either increased or decreased on that portion of the filament which is within the plating bath. Even relatively slight increases or decreases in the tension of the filament within the plating bath, e.g., as little as 50 pounds per square inch, will be sufiicient to destroy the ordered nucleation of the elecrodeposited metal and initiate random nucleation of the electroplate.

When the electroplating is carried out in the manner which has been described, following the pretreatment of the filament as has been set forth hereinabove, the resulting plated filament produced is found to have exceptionally high strength. Moreover, the increase in tensile strength imparted to the non-conductive filament by a given cross-sectional area of electroplated metal is appreciably greater than the increase in tensile strength imparted by this same cross sectional area of electroplated metal when it is plated on a highly conductive substrate, such as metal wire. Thus, the filaments produced by the method of the present invention have a significantly higher ratio of tensile strength to weight than do metallic fibers or filaments.

The following examples illustrate certain preferred embodiments of the present invention. Unless otherwise indicated in the specification and the claims, all parts and percentages used herein are by weight and all temperatures in degrees centigrade.

Example 1 A denier polypropylene monofilament was subjected for 2 minutes to molten phosphorus at 60-65 degrees centigrade and thereafter for 5 minutes to a 5 percent solution of nickelous acetate, also containing ammonium hydroxide and sodium hydroxide, at 70 degrees centigrade. A conductive metal phosphide was produced on the monofilament, however, the deposit was somewhat uneven.

Example 2 Example 1 was repeated except that the molten phosphorus was replaced by a 2 percent solution of white phosphorus in trichloroethylene. A conductive metal phosphide was produced on the monofilament, however, the coverage of the filament was slightly uneven.

Example 3 A 15 denier polypropylene monofilament (1.8 mils in diameter) was subjected for 5 minutes at 15-65 degrees centigrade to a 2 percent solution of white phosphorus and trichloroethylene and then for 90 seconds to molten phosphorus. Thereafter, the monofilament was transferred to an ammonical solution containing 5 percent of nickelous acetate for 5 minutes at 75 degrees centigrade. The resulting treated monofilament had a conductive metal phosphide formed at its surface which was adherent and uniform.

The foregoing process was repeated except that the treatment time in the molten phosphorus was decreased to seconds. A conductive adherent, uniform metal phosnhide was formed at the surface of the monofilament.

Example 4 A 15 denier polypropylene monofilament was subjected to 1 /2 minutes to a 2 percent solution of which phosphorus and trichloroethylene at degrees centigrade and thereafter for 1 /2 minutes to molten phosphorus at 65 degrees centigrade. The monofilaments were then subjected for 5 minutes to a solution containing 5 percent nickelous acetate, 5 percent ammonium hydroxide and 1 percent sodium hydroxide at degrees centigrade. A conductive, adherent, uniform nickel phosphide was produced at the surface of the substrate.

Comparison of Examples 1-4 show that the metal phosphide obtained when a combination of molten phosphorus and a solution of phosphorus is employed is superior to the metal phosphide when either treatment is employed individually.

Example 5 A 15 denier monofilament of a polypropylene fiber (1.8 mils in diameter) was subjected for 5 minutes to a 2 percent solution of yellow phosphorus and trichloroethylene at 55 degrees centigrade and then for 30 seconds to molten phosphorus. The thus-treated monofilament was thereafter subjected for 5 minutes to a solution containing 5 percent nickelous acetate, ammonium hydroxide and sodium hydroxide at 70 degrees centigrade. The monofilament was electroplated with semi-bright nickel by employing a current density of 50 amperes per square foot for about 30 minutes. Measurement showed that the semibright nickel had added 0.45 mil to the diameter of the filament. The tensile strength of the treated monofilament was tested on a Instron tester and found to be 125,000 pounds per square inch of metal cross-section which is more than 155 percent of the normal nickel tensile strength of 80,000 pounds per square inch. During the electroplating, care was taken so that the monofilament was not subjected to any continuous or momentary change in deformation tension.

Example 6 A 15 denier monofilament of polypropylene fiber was degreased by soaking overnight in kerosene. The monofilament was immersed for 7 minutes in an degree centigrade solution of 2 percent yellow phosphorus and trichloroethylene, withdrawn into the air for 3 minutes and then immersed for 7 minutes in an ammonical solution of nickel sulfate. The resulting monofilament had an adherent metal phosphide on its surface and was electroplated in a Watts nickel bath at 60 degrees centigrade for 30 minutes. Measurement showed that the Watts nickel had added 0.20 mil to the diameter of the filament. An Instron tester showed that the tensile strength of the thus-treated monofilament Was 160,000 pounds per square inch of metal cross section. During the electroplating care was taken so that the monofilament was not subjected to any continuous or momentary change in deformation tension in the area of deposition.

Example 7 A nylon monofilament was subjected for 1 minute to a saturated solution of trihydroxymethylphosphine in a 1:1 benzene-ethanol solution at 25 degrees centigrade and then pressed dry. The treated monofilament was thereafter subjected for 2 minutes to a 5 percent silver nitrate and NH OH solution at 55-60 degrees centigrade.

Example 8 A 20 mil polyvinyl chloride monofilament was immersed in a 2 percent solution of yellow phosphorus in trichloroethylene at 55-60 degrees centigrade for 5 minutes and then in molten phosphorus for 30 seconds. Thereafter the monofilament was immersed in a percent solution of nickel acetate also containing NH OH and NaOH at 70-75 degrees centigrade for 5 minutes. The resulting article had a conductivity of 3,500 to 8,000 ohms.

Example 9 Example 8 was repeated except that the diameter of the monofilament was 14.5 mils, immersion in the phosphorus solution was for 20 seconds, immersion in the molten phosphorus was for 27 seconds, and immersion in the nickel solution was for 3 minutes.

Example 10 A 20 mil polyvinyl chloride monofilament is immersed in a solution prepared by mixing one mole of white phosphorus and one mole of lithium ethoxide in 600 milliliters of ethanol. After 30 seconds in the low oxidation state phosphorus solution at room temperature, the monofilament is washed with water for 30 seconds and immersed in a 5 percent ammonical solution of nickel chloride at room temperature for minutes. An adherent nickelphosphorus coating is formed.

Example 11 Each of the monofilaments resulting from the processes of Examples 7 to 10 inclusive are electroplated into high strength filaments by employing a semi-bright nickel plating solution of 50 amperes per square foot for about 30 minutes and not subjecting the monofilaments to any change in deformation tension, continuous or momentary, during the electroplating process.

Example 12 A Saran monofilament of 0.006 inch diameter was immersed in a solution of perchloroethylene for 2 minutes at 64 degrees centigrade. The monofilament was thereafter air dried for 1 minute and subjected to a solution of 1 percent P 8 in perchloroethylene for 7 minutes at 60 C. The thus treated monofilament was thereafter air dried for 6 minutes and subjected to a solution of 0.04 M CuCl 0.16 Methylene diamine/ 0.32 M NaOH for minutes at 60 degrees Centigrade. The thus treated monofilament was thereafter air dried for 1 minute and rinsed in distilled water for 1 minute.

Example 13 A Saran monofilament treated in accordance with Example 12 was placed in a conventional commercial bright nickel electroplating bath containing from about 10.8-14.2 oz./gal. nickel, 2.4-3.6 oz./gal. chloride and 6.0-6.5 oz./ gal. boric acid and as brighteners, a 2 gram/l Saccharin, 4 grams/l allylsulfonate and 75 mg./l butyne diol for 2 hour at 9 milliamps and a temperature of 55 degrees centigrade, while not subjecting the filament to any change in deformation tension. The resulting electroplated filament had a plate thickness of 1.9 mils, and a tensile strength of 244,000 p.s.i. of metal cross section.

Example 14 A Saran monofilament was treated in accordance vw'th Examples 12 and 13, except that the electroplating was for 1 /2 hours at 12 milliamps. The resulting electroplated filament had a plate thickness of 1.5 mils, and a tensile strength of 252,000 p.s.i. of metal cross section.

Filaments, when treated according to this invention, are characterized by the deposited metal possessing greater tensile strength than the same deposited metal possesses when plated on a highly conductive substrate, such as a copper wire. This increase in tensile strength can be 50% to 300% or even greater.

Various changes and modifications can be made in the process and products of this invention without departure from the spirit and scope of the invention. The various embodiments of the invention disclosed herein serve to further illustrate the invention but are not intended to limit it.

What is claimed is:

1. In the process for producing a plated filament wherein a polymeric filament, having a non-macroporous surface, is treated with an organic solvent solution of material selected from elemental white phosphorus and low oxidation state phosphorus compounds, in which the organic solvent of said solution is one which is capable of swelling the surface of said filament without detrimentally affecting it, the resulting filament is treated with a metal salt or a complex thereof in which the metal is selected from Group IB, IIB, IVB, VB, VIB, VIIB, VIII of the Periodic Table and the resulting treated filament is then electroplated, the improvement which comprises effecting the electroplating so that that a portion of the filament within the plating bath is maintained free of deformation tensions and changes in deformation tensions which cause random nucleation of the metal being electrolytically deposited, whereby an electroplated filament is formed having on its surface an adherent, electrolytically deposited metal coating having an ordered nucleation.

2. The process as claimed in Claim 1 wherein the filament is treated with elemental White phosphorus.

3. The process as claimed in Claim 2 wherein following the treatment with the solution of phosphorus in a solvent, the filament is treated with molten elemental white phosphorus.

4. The process as claimed in Claim 1 wherein the filament is pretreated with a solvent prior to the treatment with the phosphorus or phosphorus compound.

5. The process as claimed in Claim 1 wherein the filament is treated with phosphorus sesquesulfide.

6. A high strength filament comprising a filament of a non-macroporous polymeric material having on the surface thereof an adherent metal phosphide and having on the surface of said adherent metal phosphide an adherent electrolytically deposited metal coating, having an ordered nucleation.

7. A high strength filament comprising a filament of a non-macroporous polymeric material having on the surface thereof an adherent metal-phosphorus-sulfur compound and having on the surface of said compound an adherent electrolytically deposited metal coating having an ordered nucleation.

References Cited UNITED STATES PATENTS 3,235,473 2/1966 Le Duc 204-30 3,282,737 11/1966 Hinterman et a1. 136-120 2,650,708 3/ 1972 Gallagher 204-30 3,642,584 2/1972 Quinn et a1. 204-3-0 3,607,681 9/1971 Cooke et al. 20430 OTHER REFERENCES Principle of Elecroplating and Electroforming, by Blum et al., 3rd ed., 1949, pp. 60-69.

Modern Electroplating by Lowenheim, 2nd ed., 1963, p. 680.

J. H. MACK, Primary Examiner R. L. ANDREWS, Assistant Examiner 

1. IN THE PROCESS FOR PRODUCING A PLATED FILAMENT WHEREIN A POLYMERIC FILAMENT, HAVING A NON-MACROPOROUS SURFACE, IS TREATED WITH AN ORGANIC SOLVENT SOLUTION OF MATERIAL SELECTED FROM ELEMENTAL WHITE PHOSPHORUS AND LOW OXIDATION STATE PHOSPHORUS COMPOUNDS, IN WHICH THE ORGANIC SOLVENT OF SAID SOLUTION IS ONE WHICH IS CAPABLE OF SWELLING THE SURFACE OF SAID FILAMENT WITHOUT DETRIMENTALLY AFFECTING IT, THE RESULTING FILAMENT IS TREATED WITH A METAL SALT OR A COMPLEX THEREOF IN WHICH THE METAL IS SELECTED FROM GROUP IB, IIB, IVB, VB, VIB, VIIB, VIII OF THE PERIODIC TABLE AND THE RESULTING TREATED FILAMENT IS THEN ELECTROPLATED, THE IMPROVEMENT WHICH COMPRISES EFFECTING THE ELECTROPLATING SO THAT THAT A PORTION OF THE FILAMENT WITHIN THE PLATING BATH IS MAINTAINED FREE OF DEFORMATION TENSIONS AND CHANGES IN DEFORMATION TENSIONS WHICH CAUSE RANDOM NUCLEATION OF THE METAL BEING ELECTROLYTICALLY DEPOSITED, WHEREBY AN ELECTROPLATED FILAMENT IS FORMED HAVING ON ITS SURFACE AN ADHERENT, ELECTROLYTICALLY DEPOSITED METAL COATING HAVING AN ORDERED NUCLEATION. 